a) Field of the Invention
The present invention relates to a conical hydrodynamic bearing device in which a conical shaft bush and a conical bearing sleeve are relatively elevated and rotatably supported in a non-contact manner by the dynamic pressure of the lubricant fluid, a recording disk driving device equipped with such a bearing device, and a method of manufacturing a conical hydrodynamic bearing device.
b) Description of the Related Art
In recent years, hydrodynamic bearing devices in which various bodies-to-be-rotated can be supported at a high speed rotation in a stable manner have been developed. In one such device, a conical hydrodynamic bearing device, as illustrated in FIG. 1 showing an embodiment of the present invention, a shaft bush 21 having a conical inclined dynamic pressure surface is relatively rotatably inserted into a shaft sleeve 13 having a conical inclined dynamic pressure surface, and lubricant fluid such as oil is filled in the conical inclined bearing space which is created in the gap between the inclined dynamic pressure surface of the bearing sleeve 13 and the inclined dynamic pressure surface of the shaft bush 21.
Then, a dynamic pressure generating means (not illustrated) composed of properly shaped recessed grooves is cut on at least one of the inclined dynamic pressure surfaces of the shaft bush 21 and bearing sleeve 13. When the shaft bush 21 and the bearing sleeve 13 are relatively rotated, lubricant fluid is pressurized by the dynamic pressure generating means to generate dynamic pressure. Using the dynamic pressure of the lubricant fluid, the shaft bush 21 and the bearing sleeve 13 are relatively elevated in both the radial and thrust directions so that both members 21 and 13 are rotatably supported in a non-contact manner (for example, patent references 1 through 4).
Patent Reference 1: JP H7-7886 Publication
Patent Reference 2: JP H10-339318 Publication
Patent Reference 3: JP 2002-174226 Publication
Patent Reference 4: JP 2003-97547
As mentioned above, in a conical hydrodynamic bearing device, the dynamic pressure surfaces formed on the bearing sleeve and shaft bush are inclined with respect to the rotary shaft; in order to obtain a good dynamic pressure property such as the amount of relative float of both members, it is necessary to precisely establish a manufacturing tolerance for the angle of the inclination of the dynamic pressure surfaces to form the inclined dynamic pressure surfaces with high precision. Thus, the manufacturing of such inclined dynamic pressure surfaces requires time and poses problems.
Because the inclined dynamic pressure surface on the bearing sleeve and that on the shaft bush extend parallel to each other with the same inclination angle, even a small manufacturing error may greatly degrade the dynamic pressure property, possibly causing seizure and the like. For this reason, the yield decreases, resulting in expensive products.
Problems to be Solved
Since, in the above-mentioned conical hydrodynamic bearing device, the inclined dynamic pressure surfaces formed on the bearing sleeve 13 and shaft bush 21 are in the positional relationship in which they are opposed to each other while they incline in the axial direction, the positions of both members 13 and 21 in the axial direction are greatly changed even with a small manufacturing error.
Therefore, it is necessary to establish the manufacturing tolerance for the angle of the inclined dynamic pressure surfaces to be extremely precise to form the surfaces with high precision.
For example, when the bearing sleeve 13 and the shaft bush 21, formed with a proper precision as illustrated in FIG. 13, are coupled with each other, the gap between the fixed member and the rotary member in the axial direction, especially, the reference gap, AD, in the axial direction between stopper members 25 and 13d for a rotary hub 22 provided on the shaft bush 21 and the bearing sleeve 13 is maintained at a suitable gap (20 μm, for example). Consequently, backlash in the axial direction in the device on the whole can be prevented.
On the other hand, as illustrated in FIG. 14, if the outer diameter of the shaft bush 21 is formed even a little larger due to a manufacturing error, the shaft bush 21 is shifted from the bearing sleeve 13 to the upper side in the axial direction, causing an axial backlash in the entire device. When such an axial backlash occurs in a recording/reproducing disk rotation driving device, for example, the recording/reproducing disk may make contact with the recording head, possibly damaging it. For this reason, in the example of FIG. 14, a stopper member 25 on the rotary hub 22 is attached via a spacer 26 having a thickness that corresponds to the above-mentioned axial displacement. With this, the reference gap AD in the axial direction is maintained properly.
As mentioned above, it is necessary to form highly precise inclined dynamic pressure surfaces in order to manufacture a conical hydrodynamic bearing device, thus requiring more time and failing to prevent a decrease in the yield. As a result, the device becomes expensive.